LED devices are semiconductor photonic devices that emit light when a voltage is applied. LED devices have increasingly gained popularity due to favorable characteristics such as small device size, long lifetime, efficient energy consumption, and good durability and reliability. In recent years, LED devices have been deployed in various applications, including indicators, light sensors, traffic lights, broadband data transmission, back light unit for LCD displays, and illumination apparatuses. For example, LED devices are often used in illumination apparatuses provided to replace conventional incandescent light bulbs, such as those used in a typical lamp.
One of the performance criteria for LED illumination apparatuses is light output uniformity. For example, it is desired that the light output for an LED illumination apparatus maintain relatively uniform color and brightness throughout different areas of the LED illumination apparatus. However, existing LED illumination apparatuses often suffer from poor light output uniformity, or may require expensive fabrication costs to achieve sufficient light output uniformity.
Therefore, although existing LED illumination devices are generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect. A low cost LED illumination apparatus having good light output uniformity continues to be sought.